Fix: sessiond: previously created channel cannot be enabled

Observed issue ============== A previously created channel cannot be enabled back once a session is started. Cause ===== The check validating that the session was started is to early in the `cmd_enable_channel` function. Solution ======== Move the check at the creation code path when the channel is not found. Known drawbacks ========= None. Signed-off-by: Jonathan Rajotte <[email protected]> Change-Id: I8e7d62b7e97246e65f1cf9022270293a6dd34cc9 Signed-off-by: Jérémie Galarneau <[email protected]>
lttng · Oct 18, 2021 · 11ab4ae · 11ab4ae
1 parent aa02346
commit 11ab4ae
Showing 1 changed file with 18 additions and 9 deletions.
diff --git a/src/bin/lttng-sessiond/cmd.c b/src/bin/lttng-sessiond/cmd.c
@@ -1387,15 +1387,6 @@ int cmd_enable_channel(struct ltt_session *session,
 
 	rcu_read_lock();
 
-	/*
-	 * Don't try to enable a channel if the session has been started at
-	 * some point in time before. The tracer does not allow it.
-	 */
-	if (session->has_been_started) {
-		ret = LTTNG_ERR_TRACE_ALREADY_STARTED;
-		goto error;
-	}
-
 	/*
 	 * If the session is a live session, remove the switch timer, the
 	 * live timer does the same thing but sends also synchronisation
@@ -1444,6 +1435,15 @@ int cmd_enable_channel(struct ltt_session *session,
 		kchan = trace_kernel_get_channel_by_name(attr.name,
 				session->kernel_session);
 		if (kchan == NULL) {
+			/*
+			 * Don't try to create a channel if the session has been started at
+			 * some point in time before. The tracer does not allow it.
+			 */
+			if (session->has_been_started) {
+				ret = LTTNG_ERR_TRACE_ALREADY_STARTED;
+				goto error;
+			}
+
 			if (session->snapshot.nb_output > 0 ||
 					session->snapshot_mode) {
 				/* Enforce mmap output for snapshot sessions. */
@@ -1503,6 +1503,15 @@ int cmd_enable_channel(struct ltt_session *session,
 
 		uchan = trace_ust_find_channel_by_name(chan_ht, attr.name);
 		if (uchan == NULL) {
+			/*
+			 * Don't try to create a channel if the session has been started at
+			 * some point in time before. The tracer does not allow it.
+			 */
+			if (session->has_been_started) {
+				ret = LTTNG_ERR_TRACE_ALREADY_STARTED;
+				goto error;
+			}
+
 			ret = channel_ust_create(usess, &attr, domain->buf_type);
 			if (attr.name[0] != '\0') {
 				usess->has_non_default_channel = 1;